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arm64: nofpsimd: Handle TIF_FOREIGN_FPSTATE flag cleanly

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commit 52f73c383b2418f2d31b798e765ae7d596c35021 upstream

We detect the absence of FP/SIMD after an incapable CPU is brought up,
and by then we have kernel threads running already with TIF_FOREIGN_FPSTATE set
which could be set for early userspace applications (e.g, modprobe triggered
from initramfs) and init. This could cause the applications to loop forever in
do_nofity_resume() as we never clear the TIF flag, once we now know that
we don't support FP.

Fix this by making sure that we clear the TIF_FOREIGN_FPSTATE flag
for tasks which may have them set, as we would have done in the normal
case, but avoiding touching the hardware state (since we don't support any).

Cc: stable@vger.kernel.org # v4.14
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Suzuki K Poulose 2020-02-14 15:19:37 +00:00 committed by Greg Kroah-Hartman
parent 06fb1c6d23
commit afe95b7f56
1 changed files with 13 additions and 2 deletions
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15
arch/arm64/kernel/fpsimd.c
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@ -206,8 +206,19 @@ void fpsimd_preserve_current_state(void)
*/
void fpsimd_restore_current_state(void)
{
if (!system_supports_fpsimd())
/*
* For the tasks that were created before we detected the absence of
* FP/SIMD, the TIF_FOREIGN_FPSTATE could be set via fpsimd_thread_switch(),
* e.g, init. This could be then inherited by the children processes.
* If we later detect that the system doesn't support FP/SIMD,
* we must clear the flag for all the tasks to indicate that the
* FPSTATE is clean (as we can't have one) to avoid looping for ever in
* do_notify_resume().
*/
if (!system_supports_fpsimd()) {
clear_thread_flag(TIF_FOREIGN_FPSTATE);
return;
}
local_bh_disable();
@ -229,7 +240,7 @@ void fpsimd_restore_current_state(void)
*/
void fpsimd_update_current_state(struct fpsimd_state *state)
{
if (!system_supports_fpsimd())
if (WARN_ON(!system_supports_fpsimd()))
return;
local_bh_disable();